What is the problem with this, exactly?
First, trying to detect magic takes a full minute. Hardly a very quick and convenient thing to do.
Second, why is magic's presence cheapened by an easier ability to perceive it? Just because people can perceive magic doesn't mean it became any more commonplace for magic to actually be present.
Third, you handle an odd definition of "balance". Being able to detect magic doesn't help anyone overcome monsters or obstacles, especially since you can't casually walk and detect at the same time.
Detect magic ability, in all other editions of the game, are a very limited resource. It's something you might do when you are at a treasure horde and have to pick and chose what to carry home, or when you think there may be a magical trap or effect but need confirmation, yay or nay, to make a better decision.
My answer to your question about my use of the term "balance" is similar to my answer about why it is a bad thing to allow at-will magic scanning.
Okay, so there are 1440 minutes per day, so in theory in 4e you could only use Arcana to detect magic 1440 times maximum, but in real terms, let's be honest here, it's virtually unlimited. I've been in several exploration situations in different groups where arcana was used like a tricorder to scan for magic items,
in every single room of the dungeon. And before you say that's cheesy, that's exactly what adventurers hunting treasure
should be doing as a matter of course, using their abilities to their maximum benefit, similar to the ten foot pole used to check for traps in previous editions. In fact, it was used to "clean" dungeons of magic loot post monster wipage. It removes the selective, discriminate use of detection spells and reduces it to basically, all magic items in the dungeon might as well be glowing.
That is what I dislike about it.
This is an affront to the "exploration" pillar, since it removes mystery and any chance of failure (i.e. missing any magic items in a dungeon). In other editions a M-U could only scan detect magic a few times, and must be selective about which rooms to do it in. This allows for the possibility of failure. Again, yet another instance of why 4e, might seem at first to have offered an innovation in this department, but actually was just a lazy hack to speed up exploration in favor of getting quicker to the next encounter. This is unbalanced. I've seen it in too many 4e games to not see a pattern, and after a while you realize it's baked into the assumptions of rules, the power frequency, and yes, even the skills.
Everybody knows Arcana + Perception are the two uber skills in 4e to have. They are used waaaaaay more often than the others. That's pretty much the definition of unbalanced. Look at the color-coded guides for skill selection in the Wotc official build/ Char Op board threads, arcana is rated sky blue for most int-based classes, and would be so even for all classes, if there were more of a chance of failure. That is a sign of inbalance / OPness.
4e is not balanced, and worse than other editions. It is completely lop-sided in favor of the combat pillar of gameplay, and even skills and utility powers also push the character in that direction. By making it very hard to fail (if not impossible) to find a magic item in a horde amongst thousands, or a magic ring in a room full of dung (true story...our rogue picked up arcana precisely to be able to do this type of "metal detector" for magic items...like those bums on the beach). It is obscene IMO and a perversion of the spirit of D&D, to allow at-will detect magic.
And before any of you assume I am just harping against 4e for this, if DDN allows at-will detect magic I will be similarly dismayed. Knowing there is magic there is half the battle. (or all of it...if you're low on HP, return later...the presence of magic is often bad news when it's at the mouth of a toothy cave entrance and glows red).
One more point : Is not Arcana used for dispell magic too? yet another reason for it being OP. It's like, players are not supposed to ever have to double back, it's always onward to the next encounter-type design. It gets tiring after a while. Just because I know there are strings holding up the puppets around me virtual environment, doesn't mean I need to see them. Arcana checks remove too much power from the DM, since he can never hide anything from PCs. I.e. there is no chance of failure. And yes, at-will with a 1-minute casting time is virtually unlimited.
arcana arcana arcana skill checks. /sigh. I've heard it way too much. They broke their own rules by not even making detect/dispell magic an official at-will power for wizards, but instead hid it inside a feat. And why the 1 minute duration???? What if I absolutely must know if that object is magical ---right now? during combat? CANNOT BE DONE in 4E.
And y'all wonder why I think those rules are busted and on rails. The system is dead...RIP ...why are we even discussing this??? We can make a poll and ask if detect magic should be at-will or not...it's HUGELY powerful to know where magic is at no cost. While others search the room, the wizard scans, it doesn't slow the party down at all, it just makes it an "automatic action". Anything that's an automatic thing to do is a sign of OP ness. Way too powerful for one feat too, or even for free at level 1 for a wizard (or likely, at any level). I just really find magic in 4e felt unmagical, mundane, and frankly, too commonplace and boring. Do not want in DDN. Let's keep some mystery going.
Life shouldn't be convenient for PCs, there shouldn't be bright green arrows pointing to every clickable/worthwhile item
onmouseover in the dungeon.